Goal of the Study: The goal of this study is to use optical stimulation of the BLA-mEC axon terminals to determine if this activation can alter the consolidation of cued-response learning.

Methods: We transduce male Sprague-Dawley rats with ChR2 which allows for the expression of light sensitive opsin channels. There is a four-week period in between the virus surgery and optic implants because it allows for the expression of the opsins. After the optic implant surgery, a Barnes maze was used to assess the cued-response learning. The Barnes maze consisted of an open, raised circular platform with a series of ports along the periphery, one of which led to an escape chamber. During the training trials, the escape port was marked with a distinct cue immediately above it, and the port and cue were moved in unison to a different cardinal direction for each trial to prevent the animal from using a spatial strategy to solve the task. On day 1 (training), rats were given 8 training trials on the cued-response learning task, followed immediately by 15 min of optical stimulation of the BLA-mEC pathway. Stimulation was given in the theta-frequency range (2 s bursts of 8 Hz stimulation, every 10 s). On day 3, rats were returned to the Barnes maze for a single retention test in which the target port, together with the cue, was located in a random cardinal direction.)

Results: The rats that had received optical stimulation took longer to find the escape port, which indicate that they had impaired retention. These findings indicate that theta-frequency stimulation of BLA-mEC projections interfered with the consolidation of cued-response learning, consistent with the hypothesis that these two neural systems compete with one another. Ongoing experiments are examining whether stimulation of the BLA-caudate pathway enhances the consolidation for cued-response learning.

Recall Results: Past research suggests that the pathway from the BLA-mEC is involved in the consolidation of spatial memory/learning, and the pathway from the BLA-caudate is involved in the consolidation of cued-response learning. Studies have shown that the activation of one of these systems impairs the consolidation of the opposite system, and therefore impairs the learning of that system.